A Schmitt Trigger (ST) is a bistable circuit in which the output changes state when the input rises above an upper threshold and again changes state when the input falls below a lower threshold. An ST thus includes hysteresis, which is useful to reject input noise and glitches. The difference between the upper threshold voltage and the lower threshold voltage is the hysteresis voltage. ST circuits are often used as input buffers to an integrated circuit. As an input buffer, the ST circuit differentiates its input signal being a logic “high” versus a logic “low”.